Ammonium nitrate blasting prills with multiple coatings and method of preparation



D. s. PARTRIDGE ETAL 3 148 095 AMMONIUM NITRATE ELASTING PRILLS WITH MULTIPLE coATINGs AND METHOD 0E PREPARATION Filed Nov. 12, 196s Sept. 8, 1964 aunzk ,232.222 KN TMW w T III Rumano: $5.96 or 052.8 22.6.:

Il TN E r\ INVENToRs mi afe 3pm/ZF ge ,WL-M5 M War/neg@ NQ w z8 5523.... 3.3183 .5w I

WN KN u? Duuu. 40:2

NMO

tate

This invention relates to a blasting mix of which the base is essential low cost fertilizer-grade ammonium nitrate. The blasting mix is so constituted that it will operate and detonate satisfactorily even in the presence of certain amounts of water.

In the preferred form of the invention a mixture of fertilizer-grade ammonium nitrate prills, together with wax and a metal, such as aluminum, which is waterproof, is utilized to provide a highly effective explosive component for use in commercial blasting operations. This combination makes a compound which is extremely efficient and which possesses many advantages over the customarily used elements.

It is a known fact that detonation causes the explosive compositions to exert sudden pressure on their surroun irs. This occurs because the substance is converted into hot gases or a volatile substance having a greater volume at the surrounding pressures than in the volume of the original explosive. The pressure is raised by the generation of heat and tms overbalances any restraining forces due to surrounding matter. A rapid expansion then tends to follow and, therefore, provides the desired effect of the blasting agent.

In any of the operations with which this invention is concerned the ammonium nitrate prills are preferably of the type customarily marketed and provided. by various commercial groups. In the preferred form of the invention fertilizer-grade ammonium nitrate prills are customarily mixed with wax and aluminum to provide a desired type of waterproof product. In the operation, the ammonium nitrate prill is first heated to a desired ternperature, after which a small percentage by weight of paraflin, also heated to a desired temperature, is added to the hot prills. The paraiiin tends to enter into the pores of the prills and in this respect sensitizes them so that they will detonate with a much lower impulse. Following this coating a mixture of wax and gilsonite heated to a selected temperature is added. The agitation or tumbling of the prill is continued for a specified time period. Following this operation, in essence, a final treatment is completed by adding a small percentage by weight of water-ground powdered mica after which the coated prills are removed from the mixer and allowed to cool. The coating of the wax and gilsonite covers the prill completely and makes it su'iciently waterproof that it is capable of being immersed in water for long periods of time without dissolving.

In a second form of the composition and in a modification of the formed explosive, after the prill has been coated with the hot parain there is then added a small percentage by weight of a paint grade aluminum following the treatment with the hot wax.

In still another form of the composition, the treatment process is generally like that last described except that following the addition of the wax a larger percentage of aluminum of considerably coarser grades is added instead of the mica. This addition gives a mixture of high energy which compares favorably with dynamite and other explosives and yet is waterproof. Still further sensitization of any of the mixtures described above may be obtained by adding sulphur either in a melted state or as a dry powder to the prills. The invention, as herein being deddd-@,095 Patented Sept. 8, i954 scribed, accordingly, has as one of its principal objectives that of providing a waterproof mixture in which the stability of the resulting blasting agent is substantially enhanced and by which the eficiency of the detonation reaction is improved by way of providing an extremely intimate contact of aluminum particles with the ammonium nitrate particles to produce the maximum heat and gas for the detonating reaction.

In the preferred form it is a further objective of the invention to provide, through the use of waxes, gilsonite, mica additions to the ammonium nitrate, a blasting agent which will make the resultant end product completely free running and at the same time carbonize it without further additions in the eld. Further, then, it is an objective of the invention to make the explosive material more resistant to sparks and flame due to the nonammable nature of the mica or aluminum type coating which coats the ammonium nitrate prills.

The accompanying drawing in its FIGURE 1 is a schematic representation of one form which the invention may assume insofar as the arrangement of the appara-tus and the ow diagram for preparing the final prills is concerned, and in its FIGURE 2 there is shown schematically the formed prill.

In the preparation of the prills for which further description will be given, the ammonium nitrate prills are of any commercial type fertilizer-grade which can be obtained from various sources, illustratively, Monsanto Chemical, U.S. Steel Co. and others. In the preparation of the :final product the ammonium nitrate prill is rst heated in any suitable type of heat exchanger to a temperature in the range between about 70 C. and 120 C., depending upon the type of final product desired. Following the heating, a small percentage by weight, say, one percent to two percent, of the paraffin, heated to a temperature in the range between C. and 175 C., is added to the hot prills. The paraffin tends to enter into the pores of the prills. If acts to sensitize them considerably so that they detonate with a much lower impulse. Usually the mixing is done by the use of some type of rotary drum or barrel type mixer which is slightly inclined in order that the prills may move through to an outlet point. The mix-ture is permitted to be tumbled for some selected time period which usually should not exceed ten (10) minutes.

Following this mixing, wax and gilsonite from a suitable mixture of petroleum about 3 to 7 percent by weight heated to a temperature in the range between 150 C. to 250 C. is added. The wax may be of a select-ed type 'but one variety which has proved particularly satisfactory is that which is known as the A145 Petroleum Wax manufactered by Sonneborne Chemical Co. This is a microcrystalline wax having a melting point of about F. with an ASTM penetration index of between 35 and 45. The wax is a pale yellow and at a temperature of about 210 F. shows the viscosity of between 60 and 70. A micro-crystalline wax of the foregoing type is described in the publication New-Wax, published by Sonneborne Chemical Co. in January 1961, and identified by Booklet H-61 where the composition is described at page 3. With the addition of the wax and gilsonite the tumbling is continued for a short time period, usually not more than ten 10) minutes, after which the process of forming the coated prills is completed by the addition of about 3 to 7 percent by weight of water-ground powedered mica. The coated prills are then taken from the mixer and permitted to cool. When so formed, the wax and gilsonite completely coat the prill to an extent such that the prill may be water-immersed for periods up to 24 hours or longer without any lappreciable quantity dissolving.

last described with the aia-8,095

additions of approximately 1% to 25% by weight of aluminum to the process.

In a third form of the invention the composition is treated essentially in the same fashion as above outlined except that following the addition of the wax it is desirable to make an addition of between 1 to 25 percent by weight of finer powdered aluminum and adding this to the mixture instead of the mica. In one preferred form the ammonium nitrate prills are heated to about 100 C. With this there is added one percent paraffin heated to about 150 C. These are combined as above stated. Here A145 Petroleum Wax in an amount of about 3% by weight and 3% gilsonite are added, the last two being heated to about 250 C. These additions are then mixed in the fashion above explained with mica (in its added state) water-ground to pass through a 325 mesh. In the second modification the general percentages are ammonium nitrate 88 percent or minus to balance, one percent paratiin plus or minus about one percent, three percent A145 Petroleum Wax plus or minus 1.5 percent, three percent gilsonite plus or minus 2.5 percent, and about six percent water-ground mica plus or minus 2.0 percent.

In the third form above explained, the composition may comprise 75 percent ammonium nitrate plus or minus to balance, one percent parain plus or minus 1.0 percent, A145 Petroleum Wax plus or minus 1.5 percent, three percent gilsonite selects plus or minus 2.5 percent, 14 percent powdered aluminum plus or minus percent, four percent water-ground mica plus or minus three percent.

Considering now a particular form of the invention as it is applied to a iiow diagram of schematic exemplified equipment and functional relationships, the heat exchanger CTI is generally designated by the numeral 11. In one form of the invention, such heat exchanger may have a capacity of about pounds of material per minute at a maximum and be provided with about 100 tubes each having a 0.5 pound capacity per minute maximum. The period of prill retention within the heat exchanger is about three minutes with the prill moving about five feet per minute within each tube. The prill is heated within the heat exchanger until its temperature at discharge is usually between 110 C. and 120 C. In one preferred form of the invention the exchanger steam pressure is maintained in the range between zero and 40 p.s.i. as a maximum. As the heated ammonium nitrate prills leave the heat exchanger they `are discharged on a transfer conveyer schematically shown at 12. This can be a conveyer of desired capacity and speed suitable for carrying the prills into a further heater mechanism 13 which is preferable and the only wellknown type of infra red heater suitable to maintain the prill temperature at about that at which it leaves the heat exchanger.

There is arranged at one side of the 'apparatus in which the prills are heated one or more paraiin and gilsonite wax melting tanks, each having a capacity usually sufficient for several hours of production. The liquid transfer with such tanks is usually by gravity feed with the function of the tank generally being that of melting the parafiin and the gilsonite-wax and raising the temperature to somewhere between 165 C. and 175 C. The wax melting tank 15 for the paraffin has its output passed through a-tube 1e into a paraffin blender 17 at the temperature to which it is heated. This is done by a heating element type sufficient to maintain the temperature of the paratiin at a constant temperature range substantially like that at which the material leaves the heater 13. The parafiin which flows out from the heating tank 15 is passed along the distribution line 116 to be mixed in the blender with the heated prills as passed outwardly from the heater and transfer conveyor through the heater unit 13. In the heating tank 15 the constant temperature is maintained generally by a thermostat type of control of standard well-known characteristics. The distribution line w Y: r

16 leading to the blender 17 is usually of copper tubing of appropriate size to maintain the desired flow. The tubing is Vusually covered with a commerci-al grade molded pipe insulation.

The blender 17 which receives the heated prills and the paraliin mixture, in one specific example, receives the prills at the stated temperature of 70 C. to 120 C. at a rate of about 18 pounds per minute. The parafiin is supplied at a temperature of about C. at about '.24 pound per minute. With a rotational speed of the blender at about six r.p.m. and an inclination angle of about seven degrees, the prills progress through the blender at a rate of about six inches horizontally for each revolution of the blender.

At the output of the blender the prills as coated with the paraffin are supplied with a gilsonite-wax coating. They are mixed with the gilsonite and wax which is heated in tank 14 and then supplied to a distribution line 1S. The mixture of gilsonite and wax also flows through a distribution line 18 which, like line 16, is of a suitable size copper tube with a heating unit associated therewith. The tubes 13 are also covered with suitable insulating material.

A further blender 19 is provided to receive the waxcoated prills constituting the output of blender 17 in such a fashion that the mixture output from the blender 17 for the assumed example is at the rate of 18.24 pounds per minute `and with this there is now mixed at the selected temperature of 250 C. to 260 C. a mixture quantity of gilsonite and wax yin lthe amount of about 1.44 pounds per minute yto make the total mixture supply of about 19.68 pounds per minute. The yrotational speed of blender 19 corresponds to that of blender 17. The angle of inclination is also about the same so that the coated prills will advance approximately another six inches horizontally for each rotation of the blender 19.

This mixture then flows to be mixed with mica from a mica feed and hopper shown at 20. Illustratively, and as one example, the mica m-ay be `supplied at about 0.96 pound per minute through any suitable screw or augertype feed conveyor. The mica is then mixed with the heated output of the blender 19 and the mix-ture is fed into a rotary cooling drum 21 by way of a suitable feed line 22. The mica tends to separate the coated prills one from the other during cooling. The cooling drum 21, like the other components described, is also preferably inclined at a slight slope of about seven degrees. Rotation of the cooling drum is maintained at about six r.p.m. so that the coated prills advance `therethrough at approximately six inches for about each drum revolution. The mixture output from the cooling drum 21 leaves this cornponent at a tempenature of about 60 C. and feeds onto anzesndless belt-type conveyor, schematically represented aft In some instances yan aluminum coating for the prills is desirable. To :achieve this, aluminum may be drawn off from storage tanks or vats 24, 2S or 25. The aluminum is -to be .allowed to adhere to the prills. It is usually paint-grade, powdered aluminum, although in some instances -a coarse grade can be used. The powdered aluminum stored in suitable hopper-s illustratively designated 24, 25 and 26 is discharged in controlled quantity into a rotatable aluminum blender 27 which then receives the output of the cooling drum 21 which is caused to bypass the belt 23.

The amount of aluminum discharged from the hoppers may be readily controlled to provide the desired external coating on the prills. The mixture, after being rotated or tumbled in the blender 27, is finally discharged onto a second transfer conveyor 28, which, like conveyor 23, leads `to a third conveyor 29. Any transferred, coated ammonium nitrate products pass along the conveyor 23 or the conveyor 2S in the direction of the inclined conveyor 29. T-lie mix and finally discharged output on the conveyor 29 is then moved toward a storage hopper conwww' ventionally shown at 30 from which the goods may be removed for packaging in any desired fashion.

The foregoing is illustrative of one preferred fonn of the invention and illus-trates a convenient and suitable manner of providing the desired coating upon the ammonium nitrate prills. From the hopper or storage component 30 the goods may be discharged by way of a conveyor 31 to be loaded in any desired fashion into bags or other carrying components and appropriately weighed on the schematic weighing scales 32.

The schematic form of the coated prills is shown by FIGURE 2 with the various layers schematically represented by appropriate legends.

Having now described the invention, what is claimed is:

1. A blasting prill comprising a core of ammonium nitrate, a paraiin coating yabout the core exterior and a covering of gilsonite and wax about the par-atlin for waterproofing and carbonizing the core material.

2. The prill claimed in claim 1 comprising, in addition, a mica coating about the gilsonite and wax and an aluminum exterior coating for `sensitization and waterproofing.

3. The prill `claimed in claim 2 wherein the ammonium nitrate core constitutes approximately 88 percent by weight plus or minus the amount to balance of the total, wherein the parain is approximately one percent, the petroleum wax `approximately 3 percent, the gilsonite approximately 3 percent, the water-ground mica approximately 6 percent and the aluminum approximately 10 percent, all by weight.

4. The method of preparing the steps of heating blasting prills comprising fertilizer-gnade ammonium nitrate prills to a selected temperature, applying a covering of paraiin heated to substantially the temperature of the ammonium nitrate prills,

tumbling the ammonium nitrate prills rand the paraiin while maintaining the heat of each substance 'at substantially its supplied temperature for establishing fa covering of paraffin about the exterior of each ammonium nitrate prill and supplying heated gilsonite and petroleum wax, also heated to substantially the temperature of the paxan covered prill, for coating, waterproofing and carbonizing the ammonium nitrate prill.

5. The method claimed in claim 4 comprising, in addition, the steps of covering the prill and its gilsonite and wax coating with a mica covering by tumbling nely ground mica land the wax and giisonite coated prill and then applying an -aluminum covering to the mica coating.

6. The method of preparing a blasting compound which comprises heating fertilizer-grade ammonium nitrate prills to a temperature in the range between 76 C. and 120 C., heating a paraihn to a temperature in the range between C. and 175 C., coating the heated ammonium nitrate prills with the heated paralin by tumbling for a selected time period approximating 10 minutes while maintaining `substantially the heat at the prill temperature, then covering the paraffin-coated ammonium nitrate prill with a mixture of petroleum wax and gilsonite heated to the range between C. and 25 C., limiting the heating period to lapproximately 10 minutes and then withdrawing the coated ammonium nitrate prills from the tumbling device.

7. The process claimed in claim 6 comprising, in addition, `the steps of coating the exterior of the formed coated prills with water-ground powdered mica.

8. The method claimed in claim 7 comprising, in addition, the step of applying powdered aluminum as coating about the mica.

No references cited. 

1. A BLASTING PRILL COMPRISING A CORE OF AMMONIUM NITRATE, A PARAFFIN COATING ABOUT THE CORE EXTERIOR AND A 